Influenza Vaccination, Pregnancy Safety, and Risk of Early Pregnancy Loss

Since 2004, the Centers for Disease Control and Prevention and the American College of Obstetricians and Gynecologists have recommended routine influenza vaccination for all pregnant women in any trimester. Maternal influenza vaccination has been shown to decrease the risk of influenza and its complications among pregnant women and their infants in the first 6 months of life. In a recent article published in Vaccine, Donahue and colleagues reported a possible association between influenza vaccination when given very early in the first trimester and spontaneous abortion. There are limited conclusions that should be drawn from this study given the case-control design as well as the small number of patients included in the subanalysis that is the basis for the report. A prior firsttrimester safety study from this group, using a similar study design, had not observed any association with spontaneous abortion, and other reports of first-trimester vaccine safety have not observed an association. The lack of a biologically plausible mechanism for the suggested association between previous influenza vaccination and early pregnancy loss is of concern. The study's reported observation is not definitive and needs be replicated in appropriately designed studies before changing clinical practice. Pregnant women are at high risk for severe influenzarelated complications, including death, and health care providers have an obligation to their patients to continue to recommend and provide influenza vaccinations.